1. Field of the Invention
The present invention relates to a method and an apparatus for image forming, and more particularly to a method and an apparatus for image forming with an improved warm-up control for fixing a toner image on a recording medium.
2. Description of the Background Art
A background electrophotographic image forming apparatus, such as a copying machine, a printer, or a facsimile machine, generally forms an electrostatic latent image on a photoconductor according to image data. The electrostatic latent image is visualized with toner to form a toner image on the photoconductor. The toner image is transferred onto a sheet and the sheet having the toner image is conveyed to a fixing unit in which heat and pressure fix the toner image on the sheet.
Such a background image forming apparatus is being required to save energy for environmental protection or compliance with various standards or regulations. To cope with such requirements, the fixing unit needs to be quickly heated to a predetermined temperature at which a proper fixing can be performed.
One example of such a background image forming apparatus includes a sensor for detecting a temperature of the fixing unit to attempt to shorten a warm-up time of the fixing unit. However, the sensor may detect the increasing temperature of the fixing unit with a delay while the fixing unit is warming up. Specifically, the temperature of the fixing unit detected by the sensor may be lower than an actual temperature of the fixing unit. Namely, even when the temperature of the fixing unit actually reaches the predetermined temperature at which a proper fixing can be performed, the image forming apparatus may judge that the temperature of the fixing unit has not reached the predetermined temperature based on the temperature detected by the sensor. As a result, the start of fixing operations of the image forming apparatus may be delayed.
In another example of such a background image forming apparatus, a time period required for the temperature of the fixing unit to reach the predetermined temperature is calculated in advance. When the calculated time period elapses, the image forming apparatus judges that the warm-up of the fixing unit is finished. However, the temperature of the fixing unit may not reach the predetermined temperature even when the calculated time period elapses when an input voltage of the fixing unit is not sufficiently high. As a result, a proper fixing cannot be performed.